This invention relates generally to turbomachines, and more particularly to the design of an enhanced heat exchanger, in the form of an air-cooled surface cooler, for use in turbomachines.
Modern turbofan/turbojet engines have an ever-increasing demand of cooling, including gearbox oil, cooling air and electronics, while at the same time their efficiency has to be pushed ever higher. Currently air-cooled oil coolers are usually plate-fin type “brick” heat exchangers that are mounted within the bypass channel to receive flow from the engine intake or bypass stream or from a separate air-intake in the nacelle. New designs have mitigated the high drag of this design due to the plate-fin exchanger sitting in the bypass channel by utilizing a surface cooler that is mounted flush with the aft fan cowling. However, the space in this region of the engine is limited and current designs utilize nearly all the available space. As a result, newer engine technologies, which have more heat that must be dissipated, will be thermally constrained due to the lack of space available onto which the cooler may be formed. In addition, current heat exchangers such as these plate-fin “brick” coolers obstruct the air flow and incur aerodynamic losses as the cooling requirements grow. These losses mean increased specific fuel consumption.
By using a surface cooler where only the cooler fins project into the engine air bypass flow, the drag of the oil cooler heat exchanger has been reduced over that of a traditional plate-fin cooler. However increasing heat loads requires that the surface cooler will need to be larger in size. Aircraft weight is a current concern in the current industry, with a decrease in aircraft weight resulting in an efficiency increase. In addition, new engines are becoming space constrained, making the size and weight of these types of plate-fin coolers prohibitive.
In an attempt to increase efficiency of these known surface coolers, it is desirable to reduce the size and costs, while increasing the heat transfer performance. Typically, increased heat transfer can be achieved by increasing the turbulence of the flow or the effective heat transfer area. By increasing the turbulence levels of the flow and thus increasing the heat transfer coefficient of the surface cooler, the cooler size can be reduced. This will provide for a decrease in the overall size and thus weight of the surface cooler and allow for a cooler of sufficient duty to fit on the engine.\
Accordingly, there is a need for an improved surface cooler having augmented heat transfer capability without unfavorable pressure drops.